How long does Erythromycin last in an agar plate

I am supplementing my agar plates with erythromycin and I left my yeast growing overnight on them. The next day, as I had hoped, I found no growth. But by the evening there did appear to be a small amount of growth. I wondered if the erythromycin had degraded after 16 hours like ampicillin does and the yeast could grow again?

I am supplementing my agar plates with erythromycin and I left my yeast growing overnight on them. The next day, as I had hoped, I found no growth. But by the evening there did appear to be a small amount of growth. I wondered if the erythromycin had degraded after 16 hours like ampicillin does and the yeast could grow again?